Bump eslint-plugin-react from 7.20.6 to 7.21.5 in /superset-frontend

Bumps [eslint-plugin-react](https://github.com/yannickcr/eslint-plugin-react) from 7.20.6 to 7.21.5.
- [Release notes](https://github.com/yannickcr/eslint-plugin-react/releases)
- [Changelog](https://github.com/yannickcr/eslint-plugin-react/blob/master/CHANGELOG.md)
- [Commits](jsx-eslint/eslint-plugin-react@v7.20.6...v7.21.5)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

superset-frontend/package-lock.json

@@ -256,7 +256,7 @@
     "eslint-plugin-jsx-a11y": "^6.3.1",
     "eslint-plugin-no-only-tests": "^2.0.1",
     "eslint-plugin-prettier": "^3.1.3",
-    "eslint-plugin-react": "^7.20.6",
+    "eslint-plugin-react": "^7.21.5",
     "eslint-plugin-react-hooks": "^4.1.2",
     "eslint-plugin-testing-library": "^3.10.1",
     "exports-loader": "^0.7.0",